'97 four cylinder

Ok, I need some ideas as to what is wrong here. The car will start and run fine for a couple days, then without warning die going down the road or not start. If it sits for a day or two, its like it never happened. What worries me is that oil appears to be coming up into the air intake (oil puddled in air filter housing). At first we thought it was electrical, but its not. Theres a loose connection at a sensor in the air filter housing (maf?) and I think its the pcv (in the valve cover) that has a hose coming loose, but I'm not sure either of those are the cause. Any ideas would be great as I'm :banghead: pissed at this car, and don't know what the problem could be (even the reputable, family friend midas guys haven't nailed it down yet).

Check pcv valve. Not sure why it's dying but oil in the breather is usually pcv or rings

Update: Replaced pcv valve, and car was smogged, and easily passed (what geo wouldn't?). But there is no o2, and I'm not sure if thats normal? The CO% is higher than average; I've got the rest of the numbers if those would indicate anything in particular?

Anything?